My pattern is OR-like : "word1|word2|word3" I have approximately 800 words.
Can it be a problem ?
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1If all you're trying to do is to find whether your input string matches one out of a list of strings, there are probably better approaches than an enormous regex. – Oliver Charlesworth Jun 15 '11 at 13:30
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4this is probably very nice example of regex misuse. – nothrow Jun 15 '11 at 13:30
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3Yes it can be a performance problem, and a problem is one word is a prefix of another word. – Kaj Jun 15 '11 at 13:35
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Could you please describe what you are trying to do? – toto2 Jun 15 '11 at 14:11
3 Answers
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You're only limited by memory and sanity. :)
vipw
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The point is, an 800-word regex like the one the OP is describing indicates a serious design flaw. Your answer implies that everything is just fine. – arshajii Jul 04 '13 at 14:02
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You might consider using the Aho–Corasick string searching algorithm. It would be much more efficient than a regex, since it's linear and optimized for your problem. It's also a way to pay respect to our fellows from 1975 !
In particular, there is this Java implementation.
Remi Mélisson
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Why should it be? No, probably not.
A regexp with 800 words indicates a design problem somewhere, I would say. Why and what for do you need 800 words?
Miki
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+1 for design problem. I'd suggest to the op to edit this question providing more detail. – Liviu T. Jun 15 '11 at 14:39
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I am in fact counting the occurrences of a list of 800 words in a corpus. Is there any better way to do it rather than with a regex ? – Johnny Jun 19 '11 at 12:02
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Yes, using `HashMap
`. Split the text on non-words (regex `\W` if I am not mistaken), which will give you an array of `String`s. Go through each element of that array. If the hash map contains the word, increase the value by 1; if not - insert the word as a key and put 1 as value. This should be more efficient, but that is only my opinion. – Miki Jun 19 '11 at 13:35